In JP-A-2003-92359, there is described a technique including: providing a power switch for each of circuit modules that a semiconductor integrated circuit includes; and making possible to selectively cut off the power source for operating a circuit module, which does not have to be made to operate, according to an operation mode. JP-A-8-228145 shows an example of an SOI type logic circuit, which is arranged so that the body of a MOS transistor that the logic circuit includes is made to float, thereby to lower the threshold voltage thereof, and the body of a power switch supplying the MOS transistor that the logic circuit includes with a source voltage and a ground potential is biased thereby to raise the threshold voltage thereof. This document says that the MOS transistor with its threshold voltage thus lowered enables a high-speed operation of the logic circuit, and the power switch with its threshold voltage thus raised can lower the power consumption in a standby state. According to JP-A-9-121152, an adjustable threshold voltage is achieved for a power switch by biasing the body of the switch with its own gate potential, and thus a large current supply capability can be attained by a lowered threshold voltage during ON state of the power switch, whereas a sub-threshold leak current can be reduced by a raised threshold voltage during OFF state of the switch.
In addition, JP-A-10-200050 discloses a semiconductor integrated circuit, in which a leak current flowing through a circuit block out of use is cut off thereby to reduce its power consumption. Further, in JP-A-2003-215214, it is stated that a voltage-fixing circuit provided between an output terminal of a functional module which serves to cut off power source and an input terminal of a functional module which does not cut off power source fixes a signal voltage to the functional module at Ground level at the time of cutoff of the power source, whereby unstable propagation to an input gate of the functional module which does not perform the cutoff of power source is prevented.